This invention relates to a communication network comprising a station which accommodates a plurality of subscribers to selectively connect the subscribers to output channels. Although a multi direction time division multiple X (MD-TDM) radio communication network will mainly be described as the communication network, this invention is applicable to any other wire communication network.
A TDM radio communication network of the type described comprises a base or control station and a plurality of stations which may be called substations or local stations and which are communicable with the base station through a sequence of output channels. In such a TDM radio communication network, the output channel sequence may be a sequence of radio channels and is divisible into up-link and down-link channel sequences which are directed from the substations towards the base station and from the base station towards the substations, respectively. Both-way or bidirectional communication is carried out between a pair of subscribers accommodated in the substation or substations by seizing and occupying one of the up-link channels and one of the down-link channels.
In the above-mentioned radio communication network, it is assumed that one of the subscribers goes off-hook when all of the up-link and the down-link channels are occupied or used without any of the up-link and the down-link channels being idle. In this event, the subscriber in question, namely, an off-hook subscriber is supplied with a busy tone and should repeat off-hook again and again before an idle channel is found out. Therefore, invalid off-hook must often be separated by the subscriber under consideration before the subscriber can carry out communication. In addition, the subscriber in question might wait for occurrence of an idle channel in vain for an unpleasingly long term.
Under the circumstances, it is preferable to automatically inform or notify the subscriber in question of occurrence of such an idle channel.
Such automatic notification of occurrence of an idle channel might result in collision of off-hook when a plurality of off-hook subscribers wait for occurrence of the idle channel.